A gas dynamic foil bearing is simple in its structure and can be produced economically. Therefore, it has been widely applied to small-sized machines. In U.S. Pat. No. 3,893,733, issued on Jul. 8, 1975, entitled "Foil Bearing Arrangements" to Silver et al., a self-pressurizing hydrodynamic foil bearing is described in which the foil bearing comprises resilient foils providing support between a movable and stationary bearing member and resilient foil supports for supporting and stiffening the foils.
A conventional thrust gas foil bearing disclosed in Soviet Union Patent No. 1754949, issued on Aug. 15, 1992, is illustrated in FIG. 1. As shown in FIG. 1, the thrust gas foil bearing includes a plate 1 attached to a base 10, support members 2 fixed on the plate 1 by welding, and elastic foils 3 attached to the supporting members 2 by welding such that the elastic foils 3 overlap as shown. Here, the elastic foil 3 has a support portion 3a which is a tail thereof and is not attached to the support member 2, and an edge 3b of the elastic foil 3 is in contact with the adjacent foil 3. The radius of curvature of the elastic foil 3 decreases from R1 to R2 toward the edge 3b. Also, a thrust disk 11 connected to a rotor (not shown), for example, a rotating shaft is placed on the elastic foils 3.
As the thrust disk 11 connected to the rotor rotates, the gas is drawn into the space between the thrust disk 11 and the elastic foils 3, thereby lifting the thrust disk 11 from the elastic foils 3. Here, the thrust disk 11 remains in contact with the elastic foils 3 until the speed of rotation thereof reaches a normal lift-off speed. At this time, the elastic foil 3 is pressed downward by the edge 3b of the adjacent foil 3 and is elastically deformed to thereby contact the upper surface of the plate 1 at the position A (FIG. 2). At the same time. the lower surface of the deformed foil 3 is in contact with and is elastically supported by the support portion 3a of the adjacent foil 3 at position B.
However, the conventional thrust gas foil bearing has several shortcomings. Since the support portion 3b supporting the adjacent elastic foil 3 is integrally formed with the elastic foil 3 of the same material, it cannot additionally provide sufficient rigidity to each foil 3 elastically deformed by the axial load. Accordingly, the elastic foil 3 is deformed downward until it contacts the upper surface of the plate 1, which causes an axial displacement of the thrust disk 11 or the rotor connected thereto to increase during the initial operation of the bearing.
Also, the damping capacity against the axial load and a bearing load capacity are poor because the elastic foils 3 contact the plate 1 during operation at normal lift-off speed. Further, the elastic foil 3 has a radius that gradually gets smaller toward the edge 3b, thereby making the manufacturing process thereof complicated and difficult.